<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="./lib/vue-2.4.0.js"></script>
</head>
<body>
    <div id="app">
        <input type="text" v-model="n1">
        <select v-model="opt">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select>
        <input type="text" v-model="n2">
        <input type="button" value="=" @click="calc">
        <input type="text" v-model="result">
    </div>
    <script>
        var vm = new Vue({
            el : "#app",
            data : {
                n1 : 0,
                n2 : 0,
                result : 0,
                opt : "+"
            },
            methods : {
                // 方式一：
                // calc(){
                //     switch (this.opt){
                //         case "+" :
                //             this.result = parseInt(this.n1) + parseInt(this.n2)
                //             break;
                //         case "-" : 
                //             this.result = parseInt(this.n1) - parseInt(this.n2)
                //             break;
                //         case "*" :
                //             this.result = parseInt(this.n1) * parseInt(this.n2)
                //             break;
                //         case "/" :
                //             this.result = parseInt(this.n1) / parseInt(this.n2)
                //             break;
                //     }
                // }

                // 方式二：不推荐用,有安全隐患
                calc(){
                    var codeStr = 'parseInt(this.n1)' + this.opt + 'parseInt(this.n2)'
                    this.result = eval(codeStr)
                }
            }
        })
    </script>
</body>
</html>